Circuit board, method of making the circuit board and improved die for making said board

ABSTRACT

Stamping a sheet of conductive foil by means of a die of a predetermined pattern against a dielectric substrate to shear out foil sections and pressing them against the substrate while applying heat through said die to the sheared sections so as to bond the sections by means of a thermal curing adhesive to the substrate. The die has a plurality of individual die elements which shear out individual foil sections. Each die element has two lateral high pressure surfaces, a recessed middle portion and two transitional surface portions between the high pressure surfaces and the middle portion. The outer edges of each die element are shearing corners or edges, with the high pressure surfaces applying the shearing forces to the foil and substrate. In one embodiment the high pressure surfaces which produce the shearing forces against the foil sheet are substantially parallel to the foil sheet being engaged, and in another embodiment the high pressure surfaces are sloped at about 45* to the surface of the foil sheet it is engaging. The transitional surfaces of each die element are convexly curved toward the recessed middle to provide a proper force distribution which declines in magnitude toward the middle die portion, and join to the middle portion with a concave curvature.

1451 Oct. 14, 1975 CIRCUIT BOARD, METHOD OF MAKING THE CIRCUIT BOARD ANDIMPROVED DIE FOR MAKING SAID BOARD [75] Inventor: Walter Weglin,Bellevue, Wash.

[73] Assignee: Jerobee Industries, Inc., Redmond,

Wash.

22 F1166; Oct. 2, 1973 21 Appl. No.: 402,816

Related US. Application Data [63] Continuation-in-part of Ser. No.145,720, May 21,

1971, abandoned.

[52] US. Cl. 72/324; 29/625; 156/251;

156/261; 174/685 [51] Int. Cl. B2lD 43/28 [58] Field of Search 72/324,325, 327, 333;

83/685; 29/622, 624, 625, 203 B, 203 D, 203 L; 225/93, 103; 113/119;174/685; 156/251,

Primary Examiner-C. W. Lanham Assistant Examiner-James R. DuzanAttorney, Agent, or Firm-Graybeal, Barnard, Uhlir & Hughes [57] ABSTRACTStamping a sheet of conductive foil by means of a die of a predeterminedpattern against a dielectric substrate to shear out foil sections andpressing them against the substrate while applying heat through said dieto the sheared sections so as to bond the sections by means of a thermalcuring adhesive to the substrate. The die has a plurality of individualdie elements which shear out individual foil sections. Each die elementhas two lateral high pressure surfaces, a recessed middle portion andtwo transitional surface portions between the high pressure surfaces andthe middle portion. The outer edges of each die element are shearingcorners or edges, with the high pressure 261 surfaces applying theshearing forces to the foil and substrate. In one embodiment the highpressure sur- References C'ted faces which produce the shearing forcesagainst the UNITED STATES PATENTS foil sheet are substantially parallelto the foil sheet 1,187,510 6/1916 Debacher 156/261 being engaged, andin another embodiment the g 1,646,613 lO/l927 Courtenay 156/251 pressuresurfaces are sloped at about 45 to the sur- 2,622,054 12/1952Franklin..... 156/251 face of the foil sheet it is engaging. Thetransitional 2,647,852 8/1953 Franklin"..-

156/26l surfaces of each die element are convexly curved 2,753,6197/1956 Franklln 29/625 toward the recessed middle to provide a properforce 2,986,804 6/1961 Greenman et 29/625 distribution which declines inmagnitude toward the 2,988,839 6/1961 Greenman et a1. 156/251 middle dieOnion and to the middle rti 3,301,730 1 1967 Spiwak et a1. 156/267 p 1p0 3,340,606 9/1967 Anderson et a1. 83/658 a concave Curvature-3,678,577 7/1972 Weglin et al 29/625 3,713,944 1 1973 Dennis et a1. 156261 10 23 Drawmg figures M 2 4 2+ l c 4 A l f F 3 30 L l x 3;] 3o 1 3+35 31 S 3a- 15 .5 Z 31 .18

US. Patent Oct. 14, 1975 Sheetl0f6 3,911,716

M/l///// o2 US. Patent Oct. 14,1975 Sheet 2 of6 3,911,716

FHGO 5 U.S. Patent Oct. 14, 1975 Sheet30f6 3,911,716

U.S. Patent Oct. 14, 1975 Sheet 5 of6 3,911,716

FIGO 115 IFIUCh l9 FIGO 118 US. Patent 0m. 14, 1975 Sheet 6 0153,911,716

2 G I F FIG 22 FIG. 21

FIG 23 CIRCUIT BOARD, METHOD OF MAKING THE CIRCUIT BOARD AND IMPROVEDDIE FOR MAKING SAID BOARD CROSS REFERENCE TO RELATED APPLICATIONS Thisis a continuation-in-part application to my pending U.S. patentapplication, entitled A Circuit Board, Method of Making the CircuitBoard and Improved Die for Making Said Board, Ser. No. 145,720, filedMay 21, 1971, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to the art of making printed circuit boards by stamping thecircuit board elements from a metal foil.

2. Description of the prior Art The prior art shows various devices andmethods for stamping out from a foil sheet a circuit pattern for aprinted circuit board. The two main methods used in the prior art formaking circuit boards by die stamping are: (a) by use of a flat face dieand (b) by use of a knife edge die.

For example, in U.S. Pat. No. 3,678,577, entitled, Composite Structureand Method of Making the Same, by Walter Weglin and Charles W.Wildebour, issued July 25, 1972, there is disclosed a method of engaginga foil sheet with a flat-faced die to shear out a circuit pattern.Simultaneously heat is applied to the foil to cause a thermal settingadhesive between the foil and a dielectric base to bond the sheared foilsections to the substrate. As another example of the prior art, U.S.Pat. No. 2,986,804, to Greenman et 211. discloses the use of a dieelement having an extended portion to also form holes in the dielectricfor terminals. Further examples of the prior art are shown in Greenmanet al., U.S. Pat. No. 3,988,839; Spiwak et al., U.S. Pat. No. 3,301,730;Anderson et al., U.S. Pat. No. 3,340,606; and British Pat. No. 745,773.

With regard to making circuit boards by die stamping with a flat facedie, one of the problems associated with the process is that it is notpossible to make circuit boards where the circuit elements are anycloser than about one-tenth of an inch from each other (measured centerline to center line). When it is attempted to make circuit boards with aflat face die with the circuit elements closer than one-tenth of aninch, the stamping die is simply not able to shear out the circuitelements. Application of greater pressure to attempt to accomplish theshearing merely results in crushing the substrate onto which the circuitelements are to be formed.

The use of knife edge dies in stamping out circuit components from afoil sheet is shown, for example, in Petri, U.S. Pat. No. 3,015,718,which illustrates a heated die having two knife edges to cut out thecircuit element. By applying pressure andheat from the die, a thermalsetting adhesive positioned between the foil material and the substratecauses the foil circuit element to be bonded to the substrate. One ofthe advantages of having a knife edge die is that the knife edge isbetter able to cut out the foil sections. However, it is difficult tokeep the knife edge sharp, and as the knife edge becomes dull, it willoftentimes stamp out thin ribbons of foil at the edge of the circuitelements, and these sometimes remain on the circuit board and cause itto short out. Another problem associated with knife edge dies is thatwhen circuit elements are being formed on a thin film, such as a plasticsheet several thousandths of an inch thick, the knife edge sometimespenetrates through the thin film so as to damage the same.

Other examples of the prior art which show various forms ofa knife edgedie are: Courtenay, U.S. Pat. No. 1,646,613; Franklin, U.S. Pat. No.2,647,853; Franklin, U.S. Pat. No. 2,622,054; and Franklin, U.S. Pat.No. 2,753,619.

Other patents showing various foil stamping methods are: Debacher, U.S.Pat. No. l,l87,5l0; Choate, U.S. Pat. No. 1,406,538; Greenman et a],U.S. Pat. No. 2,272,003; and Anderson et al., U.S. Pat. No. 3,052,832.

It is an object of the present invention to accomplish the practicalmanufacture of circuits by a die stamping process, either on a board ora thin film dielectric, where the circuit elements are relativelyclosely spaced and relatively long die life is achieved in themanufacturing process.

SUMMARY OF THE INVENTION The preferred application of the presentinvention is in making printed circuit boards, and the present inventionresides in a method of shearing out foil sections from a metal foilsheet in the formation of such boards, a die configuration to accomplishsuch method, and a circuit board made by such method and die.

In describing the method of the present invention, a foil element whichis sheared out from a foil sheet is considered as having two lateralportions at the edges of the element, a middle portion between the twolateral portions, and two transitional portions, each positioned betweena respective lateral portion and the middle portion. The foil sheet isplaced against a surface of a yielding substrate. Then the foil sheet atthe locations of the lateral portions of the pattern element to bepressed out of the foil is engaged by means of two high pressuresurfaces which press the lateral portions of the foil element moderatelyinto the substrate, with the general plane of each of the high pressuresurfaces having a substantial angular component parallel to the foilsheet. The shearing of the foil element takes place at the outer edgesof the two high pressure surfaces.

At the same time, pressure relief is provided to the foil at thelocation of the middle portion of the pattern element, while the foilsheet at the location of the transitional portions of the foil elementare engaged by, respectively, two transitional pressure surfaces, eachof which extends from a related inner portion of its related highpressure surface inwardly, with the slope of a line tangent to thetransitional surface with respect to the plane of the foil sheetincreasing in an inward direction along the transitional surface,whereby force components of said transitional surface exertedperpendicular to the plane of the foil sheet decrease in magnitude in aninward direction. The effect of this is that while an abrupt shearingforce is applied at the outer edges of the high pressure surfaces, theforces exerted by the transitional surfaces decrease at a moderate ratetoward the middle of the foil element, so that no shearing of the foiltakes place at the transitional surfaces. Further, the decrease ofmagnitude of the force exerted from the high pressure surface across thetransitional surfaces to the middle pressure relief area causes highunit loading at a relatively small area at the high pressure surfaces.Since the pressure from the pressure surfaces is distributed bothoutwardly and downwardly into the yielding substrate, and since theinitial pressure area of the high pressure surfaces are relativelysmall, the compressive forces into the yielding substrate are dissipatedat a high rate relative to the depth to which these forces are impartedinto the substrate. The over all effect of this is to causesubstantially less compressive force outwardly of the high pressuresurfaces, which better enables the substrate outwardly of the highpressure surfaces to provide an upward counter force to the downwardforce of the high pressure surfaces and thus provide a more abruptshearing action to separate the foil element from the foil sheet at theouter edges of the high pressure surfaces.

A particular die configuration of the present invention expeciallyadapted for carrying out the above de scribed method is a die having aplurality of die elements, with each die element having a die face toengage the foil sheet and shear out a related foil element correspondingin shape to the die face. The die face of each die element has twolateral or shoulder portions at the outer edges of the die element, amiddle portion, and two transitional portions, each of which liesbetween a related shoulder poriton and the middle portion. Each lateralportion provides a high pressure surface to engage the foil sheet andshear the foil sheet along the outer edges of the shoulder portion. Thehigh pressure surface of the lateral portion lies in a plane having asubstantial angular component parallel to the foil sheet it engages. Inone embodiment, the high pressure surfaces are substantially parallel tothe foil sheet and in another embodiment are angled at approximately 45to the foil sheet.

The middle portion of the die is recessed so that at most only moderatepressure is exerted by the middle portion of the die against the middleportion of the foil element being sheared from the sheet. Each of thetwo transitional portions of each die surface extend inwardly as acontinuation of its related high pressure surface and is convexlycurved, such that the slope of a line tangent to the transitionalsurface with respect to the foil surface increases in an inwarddirection along the transitional surface. As the die is pressed againsta foil sheet on a yielding substrate, the resultant forces exerted bythe transitional surface against the foil are substantiallyperpendicular to the die surface at the area of contact at which eachforce vector is exerted, so that the force component of each vector thatis perpendicular to the plane of the foil sheet decreases along thetransitional surface in an inward direction because of the increasedslope of the transitional surface in an inward direction.

In carrying out the method of the present invention by means of theabove described die, a foil sheet is placed against a yieldingsubstrate, with a thermal setting adhesive therebetween. This substratecan be a dielectric of adequate thickness (e.g. l/32 of an inch,depending on the nature of the substrate) to provide sufficient yieldfor the stamping operation, or it can be a relatively thin substrate(e.g. a thin sheet of polyethylene of perhaps 0.002 inch to 0.005 inch)placed on a backing such as fiberboard. Alternately the substrate couldbe a coating of material sufficient to produce shear on a base material(e.g. epoxy on a metal core).

This assembly (the foil sheet, adhesive and substrate) is placed on thelower plate of a press. The die is located on an upper plate of thepress and then pressed down against the foil sheet. The high pressuresurfaces of the shoulder portions of each die element first engage thefoil sheet to press the foil portions they engage down into the yieldingsubstrate a short distance, with the outer shearing edges of theshoulder portions of each die element imparting abrupt shear forces toshear out a corresponding foil section. The transitional surfaces ofeach die element engage the foil in a manner to form the foil againstits contour, with the force exerted against the foil sheet decreasingmore gradually inwardly toward the middle of the die element withoutshearing the foil. The middle recessed portion of the die elementprovides pressure relief at the middle portion of the foil section beingsheared from the sheet and at most presses moderately against the middleportion of such foil section, thus permitting higher pressure loading atthe smaller areas of the shoulder portions of each die element, therebyenhancing the shearing action of the die elements as described above.

As in some of the prior art methods, in the preferred embodiment, thedie is heated so that it simultaneously bonds the sheared foil sectionsto the substrate by means of the thermal setting adhesive as it isshearing the sections from the foil. Subsequent to shearing the foilelements against the substrate, a further operation is performed tobetter bond and/or set the foil elements in the substrate. In generalthis is accomplished by applying moderate heat and pressure to press thefoil elements into the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view showing twocircuit elements of a circuit board adapted to be made according to thepresent invention;

FIG. 2 is a vertical sectional view of a portion of a die of the presentinvention, adapted for use in a first embodiment of the method of thepresent invention;

FIG. 3 is a vertical sectional view showing a die element of the die ofFIG. 2 about to shear out a foil section;

FIG. 4 is a view similar to FIG. 3 but showing the die element havingsheared out a foil section and bonding the same to the dielectric;

FIG. 5 is a fragmentary sectional view of a circuit board having acircuit element formed by the method shown in FIGS. 3 and 4;

FIG. 6 is a view similar to FIG. 3, illustrating a second embodiment ofthe method of the present invention with the foil element being bondedto a thin flexible dielectric;

FIG. 7 is a view similar to FIG. 6, further illustrating the method ofFIG. 6 and showing the die element engaging the foil to shear out a foilsection and bond the same to the thin flexible dielectric;

FIG. 8 is a view similar to FIG. 2 illustrating a modified form of thedie of the present invention;

FIG. 9 is a view similar to FIG. 3 illustrating a third embodiment ofthe process of the present invention using the die of FIG. 8;

FIG. 10 and FIG. 11 are similar to FIG. 9, further illustrating thethird embodiment of the method of the present invention;

FIG. 12 is a view similar to FIG. 9 showing a die configuration modifiedto that on FIG. 9, and illustrating a fourth embodiment of the processof the present invention;

FIG. 13 is a view similar to FIG. 11 further illustrating the method ofFIG. 12;

FIG. 14 is a view similar to FIG. 13 illustrating a further step in themethod of FIGS. 12 and 13;

FIG. 15 is a schematic drawing of a portion of a die elementillustrating the application of forces exerted by the same;

FIG. 16 is a graph illustrating a typical vertical force distributionpattern of the die portion illustrated in FIG. 15;

FIG. 17 is a graph similar to FIG. 16 but illustrating the lateral forcedistribution of the die portion illustrated in FIG. 25;

FIG. 18 is a diagramatic view illustrating the manner in whichcompressive forces are transmitted into the substrate;

FIG. 19 is a diagramatic view illustrating the force distribution on afoil element being sheared;

FIG. 20 is a view similar to FIG. 15, illustrating the manner in whichthe die shown in FIG. 8 exerts forces against the foil being sheared;

FIG. 21 and FIG. 22 are similar to, respectively, FIGS. 16 and 17, butillustrate the vertical and lateral force distribution, respectively, ofthe die configuration shown in FIG. 8;

FIG. 23 is a view similar to FIG. 19 illustrating the force patternexerted upon the foil element by the die shown in FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a circuitboard 10 made according to the present invention, which board 10comprises a sheet or board 12 made of a dielectric material and twocircuit elements 14 and 16 made of thin foil sections bonded to thedielectric 12. It is to be understood that usually there will be agreater number of such circuit elements 14 and 16. Only two are shownhere for-convenience of illustration.

FIG. 2 illustrates a first die configuration embodying the presentinvention, which is used in the first and second embodiments of themethod of the present invention described herein. The die is designated18, with two die elements being shown at 20. Each die element 20 is amale or punching die and has a foil engaging face or die face 22 and twoside surfaces 24. Between adjacent die elements there is a recess areaor cavity 26 defined by adjacent side surfaces 24 from adjacent dieelements 20, which recess 26 functions to receive the excess foil suchas that which is sheared away between the circiut foil sections 14 and16. For purposes of description, the general plane of the die face 22,i.e. the foil-engaging plane, will be considered as a horizontal plane,while planes perpendicular thereto will be considered as vertical.

The die face 22 of each die element 20 comprises two lateral surfaceportions 28, a middle portion 30, and two transitional surface portions32, each of which is positioned between a related lateral portion 28 andthe middle portion 30. Each lateral surface portion 28 functions in themethod of the present invention as a high pressure surface to exertsubstantial shear forces to the foil sheet which it engages. Eachsurface 28 is generally planar or moderately convex, and is sopositioned as to have a substantial horizontal angular component (i.e. asubstantial angular component parallel to the foil sheet which itengages). Each high pressure surface 28 meets the side surface 24 at anabrupt corner 34 which, as will be described hereinafter, functions as ashearing corner or edge in the method of the present invention. In thepresent embodiment, with the high pressure surface 28 being nearlyparallel to the plane of the foil it engages, this shearing corner 34 issubstantially a right angled shearing corner.

The middle recessed portion 30 of the die surface 22 is in the presentembodiment positioned in a substantially horizontal plane and isrecessed moderately with respect to the high pressure surfaces 28. Eachtransitional surface 32 extends inwardly from the inner portion of itsrelated high pressure surface 28 in an inward convex curve 36 and joinsto the middle surface portion 30 at an inner concavely curved area. Thusthe overall curvature of the transitional surface 32 is in the nature ofan S curve. The slope of each transitional surface portion 32 withrespect to the horizontal plane (i.e. the plane of the foil it engages)increases in an inward direction from its related high pressure surface28, so as to form its convex surface portion 36 and decreases furtherinwardly near the middle portion 30 to form the concave portion 38.

The first embodiment of the method of the present invention will now bedescribed with reference to FIGS. 3 through 5. In FIG. 3 is shown aportion of a lower plate 42 ofa press, on which is placed a dielectricsubstrate 12. On this substrate 12 is placed a thin sheet 44 of athermal setting adhesive, and on top of this adhesive sheet 44 is placeda sheet 46 of metal foil (in the present embodiment about 0.001 inch to0.005 inch thick) out of which electrically conductive foil sections,such as those at 14 and 16, of the circuit 10 are to be formed. Theadhesive sheet 44 is desirably a sheet about 0.001 inch thick, having aquick reaction time, or the adhesive could be a lamination on the foilor the substrate. Examples of suitable adhesives are CMC-l or CMC-l060sold by Circuit Materials Corp., Hoosick Falls, New York. The dielectricsubstrate can be, for example, an FR-3 paper epoxy made by the NVFCompany, an FR-2 paper phenolic made by General Electric Company, or aG-l0 glass epoxy made be Westinghouse corp. The foil material can be,for example, one ounce electrolytic grade copper made by Gould, inc. Itis to be understood, of course, that in a single circuit board, therecould be as many as or more individual circuit elements, and for eachcircuit element (such as those at l4-and 16) which are to be formed.there is a corresponding die element 20 whose pattern (i.e.configuration) corresponds to the circuit element being formed.

The die 18, having previously been heated to a desired temperature (e.g.225F. to 275F.), for example by attaching the die to a heated platen, tocause the thermal setting adhesive sheet to become adhesive in the areaswhere the die elements 20 contact the foil sheet 46 immediatelythereabove, is then moved downwardly to engage the foil sheet 46 andpress it moderately into the substrate 12. The manner in which this isbelieved to occur is illustrated in FIG. 4.

The particular manner in which the shearing forces are exerted againstthe foil 46 and into the substrate 12 in this first embodiment can bestbe explained with reference to FIGS. 15 through 19. While the followingexplanation of the application of forces into the foil sheet andsubstrate are reasonably justified on the basis of substantialexperimental work, it is to be understood that in consideration of thequite close dimensions involved (e.g. in the order of thousandths of aninch), and the high unit pressures exerted (e.g. sometimes substantiallyin excess of one hundred thousand psi), it is difficult to ascertainwith any great precision the effect of all the phenomena involved.However, it is to be understood that regardless of the precision or lackof precision in the following explanation, the present invention hasbeen found to be a practical solution to the problem of making circuitboards by a die stamping process, with the circuit elements being closertogether than was heretofore possible while maintaining substantiallylonger die life.

Reference is now made to FIG. 15, which illustrates one side of a dieelement 20. As a preliminary consideration, it is to be understood thatas greater pressure is exerted by a die surface on a substrate, thefurther the die surface penetrates into the substrate, and consequentlythe greater is the opposite resisting force of the substrate with thedeeper penetration of the die surface. Thus since the high pressuresurface 28 penetrates furthest into the substrate, there is indicated amaximum force vector 48 which is exerted perpendicular to the surface 28into the substrate. At an intermediate location on the transitionalsurface 32, there is a force vector exerted normal to that surfaceportion, which as shown herein is approximately 45 to the horizontal,this force vector being designated 50. The magnitude of this forcevector 50 is somewhat less than the force vector 48, since thepenetration at the point 52 from which the vector 50 is exerted into thesubstrate is less than the penetration of the hish pressure surface 28.The force vector 50 can be broken into horizontal and vertical forcecomponents 54 and 56, respectively.

In addition to the force exerted normal to the surface 32 at this point28, there is a frictional force to be considered. As the die element ispressed against the metal foil, there is some tendency for the foil 46to slip along the transitional surface 32. Thus there is a frictionalforce vector 58 exerted parallel to the surface 32, and thus at thepoint 52 the force vector 58 is at right angles to the force vector 50.The magnitude of the force vector 58 is equal to the coefficient offriction between the foil 46 and the die surface 22 multiplied by theforce vector 50. On the assumption that the metal contact of the foil 46against the die surface 22 has a coefficient of friction of two-tenths(i.e. 0.2), the magnitude of the force vector 58 would be one-fifth ofthe force vector 50. In resolving these force vectors, the horizontalcomponent 60 of the force vector 58 is subtracted from the horizontalcomponent 54, while the vertical component 62 of the force vector 58 isadded to the component 56. In summing up these components, it will beobserved that as the slope of the transitional surface 32 increases,because of the substantially greater magnitude of the vector 50 incomparison with the vector 58, the resultant vertical force component,obtained by adding the component 56 and 62 decreases until the concavelycurved area 38 is reached. Further, in proceeding inwardly along thetransitional surface 32 toward the middle portion 30, the penetrationinto the substrate is less, the over all magnitude of the vectors 50 and58 decrease, which further decreases the resultant vertical forceagainst the substrate.

This is illustrated in the graph of FIG. 16 which is i1- lustrateddirectly below FIG. 15, with the points along the base line 64 of thegraph being vertically aligned with corresponding points on the diesurface 20. Obviously, the relative magnitude of the force componentswill vary, depending on a number of factors, and the particular patternillustrated in FIG. 15 is merely an approximation, illustrating thegeneral pattern.

Also, the transitional surface of the die surface 22 exerts horizontalforce components into the foil and substrate. The magnitude of suchhorizontal force components depends mainly upon the degree ofpenetration into the substrate at the particular location at which theforce is exerted and the slant of the plane of the die surface 20 at thepoint of force application. The graph of FIG. 17 provides anapproximation of the distribution of magnitude of such lateral forces.The base line 66 of the graph of FIG. 16 has a lower point 68 coincidingwith a plane (indicated at 70 in FIG. 14) coinciding with the highpressure surface 28, and the upper point 72 of the base line 66coinciding with a plane (indicated at 74 in FIG. 14) coinciding with themiddle die surface portion 30.

Another aspect of the method of the present invention is illustrated inFIG. 18. As a general consideration, when a compressive load is appliedto a substrate, the compressive force is imparted to the substrate in anoutwardly extending pattern at approximately 45 to the direction of theapplication of the force. Also, the unit pressure which is exerted atany particular level in the substrate is equal to the magnitude of theforce divided by the area over which it is distributed. Thus, withreference to FIG. 18, it can be seen that the force of the die surface28 is exerted against the substrate at a relatively small area (e.g. anarea of perhaps 0.002 inch wide, indicated at g in FIG. 18). Thus at alevel below the substrate surface a dis tance of approximately 0.001inch, where the area of the force application would be approximatelytwice that of the contact area of the surface 28, the unit pressurediminishes to about one-half that existing at the contact surface of thesubstrate. As the force is distributed down through successive levels,the unit pressure is further diminished because of the broadening of thearea of force application. Further, there are internal frictional forcesof the substrate itself which can be presumed to further diminish theapplication of force down to the substrate.

Since these compressive forces that are distributed downwardly andoutwardly from the high pressure surface 28 tend to distort thesubstrate in some proportion to the magnitude of the forces, it can beseen that the degree of distortion in the substrate diminishes at arelatively high rate downwardly. A further consideration is that thecompressive force below the high pressure surface 28 causescorresponding shear stresses in the substrate area 84 laterally of thearea of the compressive force. However, since the highest application ofpressure from the surface 28 is in the immediate area of the surface 28,the shear forces which would tend to compress the substrate area 84 arediminished at a relatively high rate in a direction outwardly of thehigh pressure surface 28.

Consideration is now given to the application of shear forces at theouter corner or edge 34 of the face 28 of the die element 20, withreference to FIG. 19. The maximum downward compressive force is exertedat the lateral high pressure surface 28. This compressive force from thesurface 28 'drops abruptly to substantially zero at the outer corner 34.To the left of the corner 34 (as seen in FIG. 19), the substrate 12exerts a substantial upward resistive force against the foil sheet 46.This force diminishes at a less abrupt rate in a direction further fromthe shearing corner 34. The net result is to impart abrupt shearingforces of sufficient magnitude at the corner 34 to shear out a foilsection along a line corresponding to the corner 34. The forces exertedby the transitional surfaces 32 provide a force pattern between thesurfaces 23 and 30 of a more gradual rate of change, to alleviate anytendency toward abrupt force changes which could cause an undesiredshear force inwardly of the shear line 34.

It is believed that simultaneously with the shearing action, thetransitional surface 32 causes some inward extrusion of the substratematerial 12 toward the middle recessed portion 30 of the die face 22. Itis believed that this alleviates to some degree a tendency for thematerial 12 to extrude outwardly from the die element 20. It is believedthat this further enhances the shearing action at the edge line 34 ofthe die element 20.

It has been found that by shearing out metal foil circuit element (suchas those at 14 and 16) in the manner described in this first embodiment,it is possible to place the circuit elements quite close together (e.g.as close as about 0.020 inch between proximate edges of adjacent circuitelements, and as close as 0.040 inch between center lines of adjacentcircuit elements), and also to form quite narrow circuit elements (e.g.width of 0.015 inch). It has been found that circuit boards can be madeeffectively and reliably in the manner described above, with a diehaving its die elements 20 dimensioned (as shown in FIG. 2) as follows:the width of the high pressure surface and transitional surface (adimension) between about 0.002 inch and 0.005 inch; the total width ofthe die 20 (b dimension) being as small as about 0.015 inch to 0.020inch; the depth of the recessed middle die face portion 30 (c dimension)being about 0.003 inch to 0.007 inch; the spacing between adjacent dieedges (d dimension) being about 0.020 inch; and the depth of the excessfoil recess between adjacent die elements 20 (e dimension) being betweenabout 0.10 inch to 0.020 inch.

FIG. 5 shown one circuit element 14 of the circuit board made accordingto the present invention. The edge portions 28 of the circuit element 14are depressed into the circuit board 12 below its top surface butgenerally parallel thereto. The middle portion 30' of the circuit boardis generally coplanar with the top surface of the substrate 12. Theadhesive layer portion 44 beneath the element 14 is cured and bonds theelement 14 to the dielectric substrate 12.

Subsequent to the above described shearing and bonding action, it isgenerally desirable to place the circuit board through a curing processby subjecting both sides of the board to moderate heat and pressure.Such a process suitable for use in the present invention is described inmy US. Pat. No. 3,678,577. This tends to form the edges 12' of the board12 adjacent the element 14 in a smooth contour with the element 14.

For some applications it is desirable to form an electrical circuitpattern on a thin flexible dielectric, such as a sheet of polyethylenein the order of 0.002 inch to 0.005 inch thick. The method ofaccomplishing this according to the present invention is shown in FIGS.6 and 7. This second embodiment of the method of the present inventionis substantially the same as that shown in FIGS. 3 and 4, except that aflexible backing is placed between the lower press plate and thedielectric sheet.

Thus, in FIGS. 6 and 7 is shown a die 18 which is the same as the dieshown in FIGS. 2, 3 and 4. There is a yielding backing material 80, suchas a press board piece at least about l/32 inch thick. On top of thisbacking plate or board is laid a thin dielectric sheet 82, such aspolyethylene or Mylar. On top of the dielectric sheet is placed athermal setting adhesive sheet 84 and a foil sheet 86 on top of that.The adhesive sheet should be one that is flexible after setting, such asa rubber base thermo plastic adhesive, for example, CMC-666, made byCircuit Materials Corp.

The heated die 18 is pressed against the foil sheet 86 as shown in FIG.6. The results are substantially the same as shown in FIG. 4, exceptthat the dielectric sheet, being a relatively tough and durablematerial, forms around the outer edge 34 of the die 20 without shearing,and the foil sections are sheared out of the foil sheet 60 as describedabove and bonded to the dielectric sheet 56. The dielectric sheetreturns to a substantially flat surface after being stretched during theshearing operation.

FIG. 8 illustrates another die configuration of the present invention,used in the third embodiment of the method of the present invention.Elements of the die of FIG. 8 corresponding to elements of the die ofFIG. 2 will be given like numerical designations, with an a suffixdistinguishing those of the die of FIG. 8.

Thus the die 18a has two die elements 20a, each of which has a die face22a and side surfaces 24a. Each die face 22a has two high pressuresurfaces 28a, a middle surface portion 30a, and two transitionalsurfaces 32a, each with a convexly curved portion 36a and a concavelycurved portion 38a.

The configuration of the die of FIG. 8 differs essentially from that ofFIG. 2 in that the two high pressure surfaces are sloped from thehorizontal (i.e. the plane of the foil being engaged). In the presentconfiguration, this slope is shown to be at about 45 to the horizontal,so that each of the two shearing corners 34a are formed by two surfacesmeeting at about a 45 angle. However, slopes greater and lesser than 45have been utilized in such die configurations. Also, it is possible, andin some instances desirable, to form the corner 34a with a thinupstanding edge of quite small dimension (e.g. a thousandth of an inchor less).

The particular advantage of the die configuration of FIG. 8 is that itis possible to make a circuit board with the element somewhat smallerand closer together (measured from center line to center line of the dieelements) than with the die configuration of FIG. 2. Thus the dieelements 20a of FIG. 8 can be made with the width of one high pressuresurface 28a and transitional surface 32a,(dimension a in FIG. 8) beingas small as 0.002 inch, the over all width of a die element 20a(dimension b in FIG. 8) being as small as 0.012 inch, the depth of themiddle recessed portion 30a (dimension c in FIG. 8) being about 0.005inch, the spacing between proximate corners 34a of two die elements 20a(dimension d in FIG. 8) being about 0.020 inch, and the depth of therecess 26a between die elements 20a (dimension e in FIG. 8) being about0.020 inch. Also the width of an upstanding edge at 34a would besomewhat less than 0.00l inch. The side walls 24a of each die element20a desirably have a slight diverging slope from the shear corners 34ato enhance removal of the excess foil from the recesses 26a.

FIGS. 9 through 11 illustrate the method of a third embodiment of thepresent invention. As in the first embodiment, a yielding substrate 12ais placed on a plate 42a, with a layer of adhesive 44a and an overlyingfoil sheet 46a being placed on the substrate 12a. The heated die element20a is then brought into engagement with the foil 46a with the dieelement 20a each shearing out respective foil sections, as illustratedin FIGS. and 11.

As illustrated in FIG. 10, initially the lateral high pressure surfaceportions 28a engage corresponding lateral sections 2811' of the foilelement 14a being sheared from the foil sheet 46a. At the furthestdownl5 scribed in further detail with reference to FIGS.

through 23. With reference to FIG. 20, it can be seen that the highpressure surface 28a exerts a force vector 48a perpendicular to thesurface 280, which in the present configuration is 45 to the horizontal.There is also a frictional force vector 58a parallel to the surface 3028a. By resolving these two force vectors 58a and 480, it can be seenthat there is a resultant vertical force component and a lateral forcecomponent, with the vertical force component being somewhat greater thanthe lateral force component due to the force contribution of thefrictional vector 58a.

Also, a second set of force vectors is indicated at point 52a on thetransitional surface 32a. Since the resolution of force components atpoint 52a is substantially the same as at point 52 in FIG. 15, furtherdescription of these force vectors and the resolution of the same isgiven herein.

FIGS. 21 and 22 correspond to, respectively, FIGS. 16 and 17, andillustrate, respectively, the vertical and lateral force componentsexerted along the high pressure surface 28a and transitional surface32a. It can be seen that in addition to the substantial vertical forcecomponents exerted by the high pressure surface 28a, there is also asignificant laterally inward'set of force components which cause theinward extrusion of the foil 46a and substrate 12a. It is believed thatthis enhances the separating action of the foil 46a at the shear lineexisting at the shear corner 34a.

The distribution of shearing forces on the foil 46a is illustrated inFIG. 23. It can be seen that at the location of the shearing corner 34a,there is an abrupt change in shear forces which causes separation of thefoil 46a. Laterally of this area of separation, the forces decline at asufficiently moderate rate so that additional separation of the foilalong these areas of force application does not occur.

The fourth embodiment of the method of the present invention isillustrated in FIGS. 12 through 14. This embodiment is adapted to cutout foil sections from a substantially thicker foil sheet than in theprevious three embodiments (e.g. as thick as 0.0135 inch). Theconfiguration of the die elements used in the method of the fourthembodiment are substantially the same as shown in FIGS. 8 through 11, sothese will not be described in detail herein. Rather, the components ofthe die shown in FIGS. 12 through 14 will be given numerical,designations similar to corresponding components shown in the die ofFIGS. 8 through 11, with a b suffix distinguishing those of the fourthembodiment.

The dimensions of each of the die elements 20b are approximately asfollows: the width of each high pressure surface 28b and its associatedtransitional surface (dimension a in FIG. 12) is approximately 0.005inch, the over all width of the die elements 20b (dimension [7 in FIG.12) is about 0.05 inch, the depth of the recessed middle portion 30b(dimension 0 in FIG. 12) is about 0.03 inch, the spacing between theproximate shearing corners 34b and two adjacent die elements 20b(dimension d in FIG. 12) is about 0.05 inch, and the depth of the recessbetween proximate die elements 20b (dimension e in FIG. 12) is about0.05 inch.

In the method of the fourth embodiment, substantially the same procedureis followed as in the prior embodiment with generally the sameapplication of forces, so these will not be described in detail hereinwith reference to the fourth embodiment. However, it should be noted, asillustrated in FIG. 13, that the portion of the foil section beingsheared out inwardly of the two lateral foil sections 2817 has atendency to extrude upwardly as at away from the surface of thesubstrate 12b. Accordingly, after the shearing out of the die elements14b, a metal plate 92 is placed against the circuit elements 14b asshown in FIG. 14. This metal plate 92, being heated, causes properbonding of the foil elements 14b through the adhesive layer 44b to thesubstrate 12b. Thereafter, a subsequent curing process may be employed,as described in my US Pat. No. 3,678,577.

EXAMPLE I A paper base epoxy substrate about 0.032 inch thick, 8 incheslong and 6 inches wide, EP-22 brand, made by NVF Company, was placed onthe lower plate of a press. A sheet ofa thermal curing adhesive about0.001 inch thick, CMC brand, made by Circuit Manufacturing Corp. wasplaced on top of the substrate. On top of the adhesive sheet was placeda sheet of copper foil, 0.00135 inch thick, electrolytic grade, made byGould, Inc. of McConnelsville, Ohio.

A metal die made of low carbon steel, was attached to the top plate ofthe press. This die had approximately 30 die elements formed thereon.Each die element had two shoulder portions and a moderately recessedmiddle portion. The average width of the foil-engaging face of eachshoulder portion was about 0.005 inch. The total width of the narrowerdie elements was about 0.020 inch. The closest spacing betweenapproximate edges of adjacent die elements was about 0.020 inch. Thedepth of the relief areas between cavities was about 0.020 irich. Themiddle recessed portion of the die element was about 0.004 inch indepth.

The die was heated to about 225F. by means of an electrically heatedplaten. The upper plate of the press with the die thereon was moved downto engage the circuit board assembly (the substrate, adhesive sheet andfoil) with a pressure sufficient to produce shear. The length ofengagement was about 50 milliseconds, after which the upper press platewas retracted. A circuit board having a pattern thereon corresponding tothe die elements of the die was formed, with the circuit elements bondedsecurely to, and pressed moderately into, the substrate, and the excessfoil between circuit elements remaining substantially free from bond tofacilitate stripping.

EXAMPLE 1] The same process was followed as described in Ex ample 1,except that a paper phenolic dielectric substrate was used instead ofthe paper epoxy substrate used in Example 1. This substrate was XPbrand, made by Synthane Taylor Company, 0.062 inch thick. A satisfactorycircuit board was attained with all circuit elements bonded securely tothe board.

EXAMPLE 111 The same process was followed as in Example 1, except that a1/32 inch pressboard pad was first placed on the lower plate of thepress. An adhesive coated dielectric film, Kapton (DduPont) 200, type F,was placed on top of the pad with the adhesive side up, and a sheet offoil, l-ounce foil by Gould, Inc., was placed on top of the dielectric.The die was pressed against this assembly to stamp out the circuitelements and bond them to the dielectric.

EXAMPLE 1V Substantially the same process was followed as in Example l,except that the die used was as shown in FIG. 8, with approximately thesame dimensions as described previously herein. The closest spacing ofcircuit elements was about 0.032 inch, measured center line to centerline of the circuit elements.

EXAMPLE V The same process was followed as in Example 1, except that thedie used had circuit elements substantially as shown in FIG. 12, withapproximately the same dimensions for the die as described previouslyherein. Also the foil sheet was about 0.0135 inch thick. The closestspacing of the circuit elements, measured center line to center line wasabout one tenth of an inch.

1 claim:

1. [n a die comprising at least one raised die element having a die faceof a predetermined pattern and adapted to be heated and to engage ametal foil on a yielding substrate in a manner to simultaneously shearout and bond a foil section corresponding to said die pattern againstthe substrate, said die face having a plane of engagement along whichthe die face engages the foil, said die element having side faces whichhave a substantial right angle component with respect to said engagementplane and which delineate said die pattern of the die element, said diehaving outside cavities on said side of the die element of a depthsufficient to receive excess foil without any significant pressing ofsuchexcess foil into bonding engagement with the substrate, theimprovement being that said die face is configured as follows:

a. said die face having an inner middle portion and two outer shoulderportions on opposite sides of the middle portion,

b. each shoulder portion having a high pressure surface portionpositioned generally in said plane 'of engagement and adapted to engagesaid foil and press the foil against said substrate, said high pressuresurface having a substantial angular component parallel to said plane ofengagement,

e. each shoulder portion forming with a proximate side face of the dieelement an outer shearing corner,

d. the inner middle portion of the die face being recessed with respectto the shoulder die face portions so as to lie moderately beneath saidplane of engagement at a depth less than that of the cavities andprovide a recess area for the foil section being sheared out by the dieelement, and

each shoulder portion joining to said middle portion along a bluntedconvexly curved transitional portion located between the middle portionand its related shoulder portion.

2. The die as recited in claim 1, wherein there is a second die elementsimilar to the first die element recited in claiam 1, said second dieelement being spaced moderately from the first die element so as to formbetween the two die elements one of said die cavities to receive excessfoil separated from foil sections formed by said first and second dieelements.

3. The die as recited in claim 2, wherein the die cavity between saiddie elements has a width of between about 0.01 to 0.05 of an inch.

4. The die as recited in claim 2, wherein the cavity between said twodie elements is about 0.01 to 0.1 of an inch deep.

5. The die as recited in claim 2, wherein said cavity has a widthbetween about 0.01 to 0.1 inch, the die elements having an overall widthof about 0.015 to 0.05 inch, the shoulder width of each die elementbeing about 0.001 to 0.01 inch, the middle portion of each die elementbeing recessed about 0.003 to 0.03 inch.

6. The die as recited in claim 1, wherein each of said shoulder portionshas a width of between about one thousandth to half a hundredth of aninch.

7. The die as recited in claim 1, wherein said middle die face portionis recessed with respect to said shoulder portions by at least about0.003 of an inch.

8. The die as recited in claim 1, wherein said die element has anoverall width between 0.01 to 0.05 inch.

9. The die as recited in claim 1, wherein each of said high pressuresurfaces is substantially parallel to the plane of engagement.

10. The die as recited in claim 1, wherein each of said high pressuresurfaces is at a substantial angle to said plane of engagement.

=l l l UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3, 911,716 Dated October 14 1975 Inventor(s) Walter eglin It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2, line 8 "U.S. Pat. No. 2,647,853" should be U.S. Pat. No.2,647,852

Column 3', line 1, after "the" (second occurance) insert high Column 6,line 44, "inc." should be Inc.

Column 9, line 10, "23" should be 28 Column 13, line 55, "said" shouldbe each Column 14, line 26, "claialn" should be claim Signed and Sealedthis twenty-fifth Day Of May 1976 [SEAL] .Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ojlalermand Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. 3,911,716 Dated October 14 1975 Inventor(s) Walter glin It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2, line 8 "U.S. Pat. No. 2,647,853" should be U.S. Pat. No. 2,647 ,852

Column 3, line 1, after "the" (second occurance) insert high Column 6,line 44, "inc." should be Inc.

Column 9, line 10, "23" should be 28 Column 13, line 55, "said" shouldbe each Column 14 line 26, "claiam" should be claim Signed and Sealedthis twenty-fifth Day 'of May 1976 [SEAL] .Attesr:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner of Parentsand Trademarks

1. In a die comprising at least one raised die element having a die faceof a predetermined pattern and adapted to be heated and to engage ametal foil on a yielding substrate in a manner to simultaneously shearout and bond a foil section corresponding to said die pattern againstthe substrate, said die face having a plane of engagement along whichthe die face engages the foil, said die element having side faces whichhave a substantial right angle component with respect to said engagementplane and which delineate said die pattern of the die element, said diehaving outside cavities on said side of the die element of a depthsufficient to receive excess foil without any significant pressing ofsuch excess foil into bonding engagement with the substrate, theimprovement being that said die face is configured as follows: a. saiddie face having an inner middle portion and two outer shoulder portionson opposite sides of the middle portion, b. each shoulder portion havinga high pressure surface portion positioned generally in said plane ofengagement and adapted to engage said foil and press the foil againstsaid substrate, said high pressure surface having a substantial angularcomponent parallel to said plane of engagement, e. each shoulder portionforming with a proximate side face of the die element an outer shearingcorner, d. the inner middle portion of the die face being recessed withrespect to the shoulder die face portions so as to lie moderatelybeneath said plane of engagement at a depth less than that of thecavities and provide a recess area for the foil section being shearedout by the die element, and e. each shoulder portion joining to saidmiddle portion along a blunted convexly curved transitional portionlocated between the middle portion and its related shoulder portion. 2.The die as recited in claim 1, wherein there is a second die elementsimilar to the first die element recited in claiam 1, said second dieelement being spaced moderately from the first die element so as to formbetween the two die elements one of said die cavities to receive excessfoil separated from foil sections formed by said first and second dieelements.
 3. The die as recited in claim 2, wherein the die cavitybetween said die elements has a width of between about 0.01 to 0.05 ofan inch.
 4. The die as recited in claim 2, wherein the cavity betweensaid two die elements is about 0.01 to 0.1 of an inch deep.
 5. The dieas recited in claim 2, wherein said cavity has a width between about0.01 to 0.1 inch, the die elements having an overall width of about0.015 to 0.05 inch, the shoulder width of each die element being about0.001 to 0.01 inch, the middle portion of each die element beingrecessed about 0.003 to 0.03 inch.
 6. The die as recited in claim 1,wherein each of said shoulder portions has a width of between about onethousandth to half a hundredth of an inch.
 7. The die as recited inclaim 1, wherein said middle die face portion is recessed with respectto said shoulder portions by at least about 0.003 of an inch.
 8. The dieas recited in claim 1, wherein said die element has an overall widthbetween 0.01 to 0.05 inch.
 9. The die as recited in claim 1, whereineach of said high pressure surfaces is substantially parallel to theplane of engagement.
 10. The die as recited in claim 1, wherein each ofsaid high pressure surfaces is at a substantial angle to said plane ofengagement.